1. Field of the Invention
The present invention relates to an organic electroluminescent device and specifically to an organic electroluminescent device that can be designed to have a simple device structure.
2. Description of the Related Art
In recent years, investigations have been made regarding a light-emitting device using a liquid crystal compound. Among such light-emitting devices, a device that can achieve high-speed response or high luminance at a low driving voltage is particularly desired. For example, Japanese Patent Application Laid-Open (JP-A) No. 2002-170685 discloses a technique of utilizing orientation characteristics of a liquid crystal compound, in which the state of the liquid crystal orientation is controlled by temperature and voltage so that the luminance of emitted light can be controlled. In such a technique, however, the liquid crystal layer needs to contain plural components including a carrier-transporting material and a luminescent material; therefore the device structure can be complicated.
Appl. Phys. Lett., Vol. 73, No. 11, 14 Sep. 1998, pp. 1595-1597 discloses a liquid crystal cell including a layer (monolayer) in which a host liquid crystal compound is doped with a fluorescent dye, wherein the host liquid crystal compound is used as a charge-transporting material. However, such a device has a complicated structure, because the fluorescent dye has no liquid-crystallinity and the host liquid crystal compound is used as the charge-transporting material. Appl. Phys. Lett., Vol. 77, No. 11, 11 Sep. 2000, pp. 1587-1589 discloses an organic light-emitting device which uses a mixture of a liquid crystal compound with a fluorescent dye in order to emit light. However, this device also has a complicated structure. Further, Appl. Phys. Lett., Vol. 72, No. 21, 25 May, 1998, pp. 2639-2641 discloses an example of a light-emitting device having a three-layer structure. However, since the device has the three-layer structure, the structure of this device is also complicated.